Gas Segregation Research Articles

A study on the scale dependence of mixing indices for Eulerian multiphase models

AbstractMixing can vary based on the scale at which the system is observed, and a mixing index that can capture the features at different length scales is desirable. In this article, we analyze the scale dependence of the mixing indices developed for Eulerian multiphase models. Relevant length scales are distinguished by filtering solid fraction fields. The scale‐dependence study is first done on manufactured fields of solid fraction to assess the performance of the mixing indices. The study is extended to a two‐dimensional CFD simulation of the segregation of a bidisperse gas–solid mixture. The local mixing index performs well in capturing the spatial variation of mixing at different scales. The scale dependence of two global mixing indices is considered in the study, where the state of mixing is defined based on statistical measures. We demonstrate that the choice of measures influences the sensitivity of mixing indices to mixing at different scales.

The role of pre-eruptive gas segregation on co-eruptive deformation and SO2 emissions

The presence of exsolved gas bubbles influences measurements of both volcanic surface deformation and SO2 emissions. In a closed-system, exsolved volatiles remain within the melt but in an open-system, the decoupled gas phase can either outgas or accumulate, leading to large variations magmatic gas fraction. Here we investigate the role of gas volume fraction and gas segregation processes on magma properties and co-eruptive monitoring data. First we use thermodynamic models of gas exsolution to model gas volume fraction and magma compressibility, and use these to calculate SO2 emissions and co-eruptive volume change. We find that volume change is equally sensitive to magma compressibility and chamber compressibility over realistic parameters ranges, and both must be considered when interpreting surface deformation data. Reservoir depth and magma composition are the dominant controls on gas volume fraction, but the initial content of H2O and S have strong influences on volume change and SO2 emissions, respectively. Pre-eruptive gas accumulation produces increased SO2 emissions and muted co-eruptive deformation, while degassing has the opposite effect. We then compare our models to a compilation of data from 20 recent eruptions where measurements of volume change, SO2 emissions and erupted volume are available. To the first order, shallow reservoirs produce smaller volume changes per volume erupted and silica-poor magmas yield greater co-eruptive volume changes than silica-rich systems, consistent with closed system degassing. Co-eruptive degassing causes high SO2 emissions during effusive eruptions. Comparison between model predictions and observations suggests that all magmatic systems experience a certain degree of outgassing prior to an eruption. Our findings are consistent with current conceptual models of transcrustal magmatic systems consisting of heterogeneous mixtures of gas and melt and have important implications for the interpretation of surface deformation and SO2 emission signals at all stages of the eruption cycle.

Study of gas and liquid separation in a closed drilling well with self-propelled drilling rigs

The article deals with the gas release in the process of drilling wells from jack-up drilling rigs. The article attempts to analyze the nature of the change in pressure at the blowout of the preventer after its closure due to gas releases on jack-up drilling rigs. Numerous observations in drilling rigs have shown that the pressure value increases rapidly to a maximum, then gradually decreases and stabilizes at a certain value. There are cases when the value of pressure increases rapidly. Then, without decreasing, it stabilizes. It is proposed that the phenomenon of gas segregation in a well, leading to an increase in pressure, has theoretical and practical significance. In addition, in a real well, a change in bottom hole pressure can occur under various conditions, if the rate of pressure growth due to gas segregation in the riser pipes is greater than the pressure rate due to the work of the formation, while part of the fluid from the well must be squeezed out into the formation. Keywords: well drilling; gas release; complications; open fountain; drilling fluid; preventer; gas segregation; oil and gas.

Constraints on magma storage conditions based on geodetic volume change and erupted magma volume and application to the 2011 and 2018 eruptions at Kirishima Shinmoe-dake volcano, Japan

We investigated magma storage conditions prior to the 2011 and 2018 eruptions at Kirishima Shinmoe-dake volcano in Japan based on the relationship between geodetic volume change of magma chamber and erupted magma volume. We derived an analytical expression for the ratio of the erupted magma volume to the geodetic volume change (“volume ratio”), which was formulated as a function of parameters related to the magma storage conditions. This expression shows that the volume ratio is strongly dependent on the effective compressibility of the magma chamber, which in turn depends on the rigidity of surrounding host rocks and shape of the chamber. For the Shinmoe-dake eruptions, the magnitude of the volume change (i.e., deflation) of a spherical magma chamber associated with lava effusion was estimated based on geodetic observations. The erupted magma volume was estimated from a SAR image analysis of the lava accumulation inside the summit crater. Based on these observations, we estimated that the volume ratio in 2011 and 2018 was 2.69 and 2.33, respectively. Substituting the estimated volume ratio into the analytical expression revealed that the observed geodetic data and volume ratio can be explained only when the magma chamber, which was assumed to be spherical, is filled with bubble-free magma. This result suggests that efficient gas segregation from the chamber occurred prior to the eruptions. Our results indicate that combining multi-observation data based on the volume ratio provides valuable information about the magma storage process, such as the behavior of the gas phase in the magma chamber.Graphical

The role of decompression history in gas bubble formation in crystal-rich silicic magma: Gas retention versus segregation

In crystal-rich magma, gas bubble formation causes magma lubrication by loosening the connected crystal framework. In contrast, if the crystal framework behaves as rigid, the gas bubbles segregate. In this study, we experimentally investigated the bifurcation between retention and segregation of gas bubbles in crystal-rich magmas under decompression. In particular, we focused on the history of decompression such as continuous, single-step, and multi-step decompressions with various degrees of each decompression step to consider the processes in the natural system. For this, the decompression experiments for hydrous rhyolitic melts with 50 vol% crystal were conducted with average rates of 10 and 80 MPa h−1 at a temperature of 800 °C. Bubble and crystal microstructures were analyzed using micro X-ray CT. Our experiments observed both retention and expansion of gas bubbles in the crystal-rich zone and permeable gas segregation. At an average rate of 80 MPa h−1 under multistep decompression, the boundary between the retention and segregation was the stepwise decompression of 5 MPa. On the other hand, the gas bubbles are retained when the degree of the stepwise decompression is larger than 20 MPa under an average decompression rate of 10 MPa h−1, resulting in the collapse of the framework. At the decompression degree <10 MPa at the rate of 10 MPa h−1, permeable gas segregation becomes dominant. Based on the experimental results, we established a regime map that predicts gas bubble retention and segregation during decompression. By applying this map to decompression rates and numbers of caldera collapses (twice) during the 1912 Katmai and 1991 Pinatubo eruptions, we infer that the magma during these eruptions experienced gas bubble formation (retention) without permeable segregation.

Solute segregation affected by transport properties during a bubble entrapment in upward solidification

Abstract The effects of transport properties on segregation of a dissolvable gas, for example, carbon dioxide in water in the presence of an entrapping bubble during upward unidirectional solidification is numerically investigated. Microporosity and inter-related solute segregation are two common defects detrimental to mechanical properties of components, especially to fatigue performance, strength and ductility. In this work, transport processes between the bubble, liquid and solid affected by mass, momentum, energy, and concentration Eqs. are solved by finite element schemes provided from the commercial COMSOL code. The results find that solute concentration in solid and liquid surrounding the pore increases with decreasing Henry's law constant and gravitational acceleration, and increasing surface tension and solid thermal conductivity. Solute gas concentration on the top free surface is insensitive to that in the pore rather than that in liquid and solid away from the pore. Apex cap becomes non-spherical affecting solidification rate and shape of the solidification front as ambient pressure at the top free surface and gravitational acceleration increase. Contact angle versus location of the solidification front predicted from this work and Abel's Eq. agrees well. Solute segregation encountered by pore formation is controllable.

Gas segregation in a pilot-scale ebullated bed system: Experimental investigation and model validation

Gas hold-up reduction inside hydroprocessors is critical to improving the efficiency of bitumen conversion. The use of internal gas/liquid segregation devices, such as recycle cups, has been the focus of much past research and development over the previous five decades. In this study, the effects of different recycle cup designs and working fluids were evaluated using a pilot-scale cold-flow ebullated bed reactor and compared to multiphase flow simulation predictions. Two recycle cup designs from the literature were fabricated using 3D printing technology and two working fluids were used: air-water and air-5 wt% ethanol aqueous solutions. The addition of ethanol helped create high gas hold-up and foaming conditions frequently observed in commercial hydroprocessors. It was observed that in foaming systems, the performance of the recycle cups deteriorated. Additionally, increasing the liquid flow rate, either through the inlet or increased recycle, resulted in diminished gas/liquid segregation efficiency. The accuracy of simulations using the two-fluid model was evaluated to predict gas hold-up in the pilot scale system as well as inside the recycle line. In the homogeneous flow regime, given the proper bubble size, the simulations predicted the gas hold-up in the column with less than 5% error. However, unlike the experimental observations, simulations did not predict any gas entrained in the recycle line, which is attributed to variation in the average bubble size and limitations of the existing momentum exchange closures.

Tephra sedimentation and grainsize associated with pulsatory activity: the 2021 Tajogaite eruption of Cumbre Vieja (La Palma, Canary Islands, Spain)

Long-lasting eruptions are of complex characterization and are typically associated with challenging risk assessment and crisis management due to the usual occurrence of multiple interacting hazards evolving at different temporal and spatial scales (e.g., lava, tephra, and gas). The 2021 Tajogaite eruption of Cumbre Vieja (La Palma) demonstrated how even hybrid events that are mostly effusive can be associated with widespread and impacting tephra deposits as a result of a complex interplay among gas flux, conduit geometry, and magma feeding rate. In this novel study, direct observations, syn-eruptive and post-eruptive sampling, and statistical analysis of pulsatory activity have been combined to provide new insights into eruption dynamics. They show how rapid gas segregation and high magma ascent rate modulated the gas flux at multiple vents, resulting in short-time fluctuations among the different explosive styles (ash-poor gas puffing, Strombolian, violent Strombolian, and lava fountaining) and unsteady tephra ground accumulation. Various size-selective sedimentation processes were also observed, including particle aggregation and ash fingers, which have impacted the overall tephra dispersal. In fact, even though both local and total grainsize distributions of selected layers, units, and of the whole tephra blanket are unimodal with a low fine-ash content, grainsize analysis of 154 samples suggests no correlation of particles &amp;lt;63 μm with distance from vents. Our analyses demonstrate the need to include a detailed characterization of all products of hybrid eruptions for a comprehensive interpretation of eruptive dynamics and to use multiple classification strategies that can capture eruptive styles at different temporal scales.

Iceline variations driven by protoplanetary disc gaps

ABSTRACT The composition of forming planets is strongly affected by the protoplanetary disc’s thermal structure. This thermal structure is predominantly set by dust radiative transfer and viscous (accretional) heating and can be impacted by gaps – regions of low dust and gas density that can occur when planets form. The effect of variations in dust surface density on disc temperature has been poorly understood to date. In this work, we use the radiative transfer code MCMax to model the 2D dust thermal structure with individual gaps corresponding to planets with masses of 0.1 MJ –5 MJ and orbital radii of 3, 5, and 10 au. Low dust opacity in the gap allows radiation to penetrate deeper and warm the mid-plane by up to 16 K, but only for gaps located in the region of the disc where stellar irradiation is the dominant source of heating. In viscously heated regions, the mid-plane of the gap is relatively cooler by up to 100 K. Outside of the gap, broad radial oscillations in heating and cooling are present due to disc flaring. These thermal features affect local dust–gas segregation of volatile elements (H2O, CH4, CO2, and CO). We find that icelines experience dramatic shifts relative to gapless models: up to 6.5 au (or 71 per cent) closer to the star and 4.3 au (or 100 per cent) closer to the mid-plane. While quantitative predictions of iceline deviations will require more sophisticated models, which include transport, sublimation/condensation kinetics, and gas–dust thermal decoupling in the disc atmosphere, our results suggest that planet-induced iceline variations represent a potential feedback from the planet on to the composition of material it is accreting.

Co-production of biofuel, bioplastics and biochemicals during extended fermentation of Halomonas bluephagenesis.

Halomonas bluephagenesis TD1.0 was engineered to produce the biofuel propane, bioplastic poly-3-hydroxybutyrate (PHB), and biochemicals mandelate and hydroxymandelate in a single, semi-continuous batch fermentation under non-sterile conditions. Multi-product separation was achieved by segregation of the headspace gas (propane), fermentation broth ([hydroxy]mandelate) and cellular biomass (PHB). Engineering was performed by incorporating the genes encoding fatty acid photodecarboxylase (CvFAP) and hydroxymandelic acid synthase (SyHMAS) into a H.bluephagenesis hmgCAB cassette knockout to channel flux towards (hydroxy)mandelate. Design of Experiment strategies were coupled with fermentation trials to simultaneously optimize each product. Propane and mandelate titres were the highest reported for H.bluephagenesis (62 g/gDCW and 71 ± 10mg/L respectively) with PHB titres (69% g/gDCW) comparable to other published studies. This proof-of-concept achievement of four easily separated products within one fermentation is a novel achievement probing the versatility of biotechnology, further elevating H.bluephagenesis as a Next Generation Industrial Biotechnology (NGIB) chassis by producing highly valued products at a reduced cost.

Application of gas-assisted gravity drainage (GAGD) to improve oil recovery of Rang Dong basement reservoir

As an option to improve the ultimate oil recovery factor of the Rang Dong field, a feasibility study of gas-assisted gravity drainage (GAGD) application was carried out for the fractured basement reservoir with a single-well Huff ‘n’ Puff pilot test applied on a high water-cut producer. This paper aims to provide an in-depth understanding about such case study, which includes details on candidate selection, gas injection scheme, on-site execution, results of flow-back, post-job review and lessons learned. &#x0D; The pilot test of GAGD was recorded with a good oil rate and low water-cut during flowing back after gas injection and shut-in for gas segregation, which suggests the positive effectiveness of GAGD to some degree. The expansion of the GAGD application to other wells and areas in the field would be encouraged in any similar situation. On the other hand, the results of this pilot test shed a light into further optimisation of the candidate selection and gas injection scheme by material balance analysis and reservoir simulation respectively.

Towards a robust CFD modelling approach for reliable hydrodynamics and mass transfer predictions in aerobic stirred fermenters

A strategy based on the Reynolds averaged two-fluid model is proved to be effective for the simulation of a turbulent gas-liquid stirred tank in the whole range of possible flow regimes, namely complete recirculation, loading, and flooding. The modelling approach is validated through the simulation of a laboratory scale tank stirred with a Rushton turbine, with superficial gas velocities ranging from 1.5 mm/s to 4.4 mm/s and specific power consumption from 39 W/m3 to 837 W/m3, since such a system in this range of operative conditions is well-characterized and several well-established correlations are available for validation purposes. The gas segregation due to the formation of aerated cavities was accounted for in the determination of the specific interfacial area available for the mass transfer and the numerical predictions of the kLa better agree with the available correlations, especially in the loading regime when clinging and ‘3–3’ cavities develop, with respect to the traditional specific interfacial area formulation that does not consider the phase segregation. Finally, starting from grid independent results, the effect of computational grid coarsening is quantified, obtaining guidelines for the affordable simulation of bioreactors of large scale.

Fatty alcohol polyoxyethylene ether sulfonate for foam flooding in high-salinity and high-temperature reservoir conditions

Foam flooding can significantly improve the sweep efficiency of gas flooding by avoiding or weakening gas segregation, viscous fingering and gas channeling through areas of high permeability. However, most conventional anionic surfactants are not suitable to be used as foaming agents due to low tolerance to either high salinity or high temperature. In this paper, an anionic-nonionic combined surfactant, fatty alcohol polyoxyethylene (3) ether sulfonate (AEO3-HS) was synthesized, and its foaming performances at different conditions were examined. The results show that the foaming performance of the AEO3-HS is sensitive to crude oil which behaves as a defoaming agent. But this can be improved by mixing with cetyl dimethyl hydroxypropyl sulfobetaine (C16HSB). In mild reservoir conditions such as dissolved in simulated Daqing connate water (45 ℃, total salinity of 6778 mg/L, pH = 8–9) the AEO3-HS/C16HSB binary mixture at an optimal mole fraction ratio (0.6/0.4) and an optimal total concentration (4 mM) gives the maximum composite foaming index of 1100 Ls by shaking 10 mL solution with 0.25 g oil in a 100 mL cylinder. Moreover, the AEO3-HS/C16HSB binary mixture is well soluble in brine with 5000 mg/L CaCl2 + 100,000 mg/L NaCl at 60 °C, and does not hydrolyze in aqueous solution when stored at 90 °C for 3 months. In addition, the AEO3-HS and C16HSB molecules show attraction in mixed monolayer and the crude oil can be easily emulsified as small oil droplets dispersed in foaming solution during foaming process, which ensures the stabilization of the pseudo-emulsion films and thereby the foam stability in the presence of crude oil. The AEO3-HS synthesized is therefore a good candidate as foaming agent for high salinity and high temperature reservoirs.

Assessment of Aquifer Performance for Oil Drainage in the Upper Pinda Reservoir of the Mibale Field

The Mibale field in offsore of the DRC has been producing oil since 1976. This field is faced with the arrival of massive water and the depletion of its reservoir leading to the drop in its oil production, while the injection of water is effective for several decades. Understanding the behavior of the aquifer in this reservoir is a solution to the application of effective water flooding for oil drainage to this field. The objective pursued in this study is to evaluate the performance of the aquifer on the basis of the material balance equation, to understand its behavior in maintaining or not the pressure in this reservoir in order to identify the causes related to this depletion and the influx of water despite the application of water flooding techniques. To reach this goal, the data collection during the internship made it possible to analyze and process this data using professional software. The results show that the overall drainage index of the water drainage mechanism is 84% (due to 20% for the aquifer alone and 64% for the water flooding) and 10% of oil compressibility. (IDOI), 6% of dissolved gas segregation (IDS). Reserves in this reservoir are estimated at 4.5 million barrels. The aquifer is inactive, semi-radial linear with a constant (U) estimated at 595.5 barrels per psi (bbl / psi) and an initial volume (WI) of 347.1 million barrels (Mbbl). Cumulative contributions from this aquifer are estimated at 173,868,933 barrels for the last 42 years of operation. This aquifer alone has no influence on the inflow of water and the maintenance of pressure, but its influence increases with water from injection wells. In conclusion, this inactive aquifer is located in the carbonate Karst of Upper Pinda to the north of the deposit. Being inactive, this aquifer is not at the origin of breakthrough or coning water acting in this field. It is likely that this phenomenon is amplified by water flooding. Which allows us to classify water flooding technology among aquifer drainage mechanisms; since this significantly activates the behavior of the aquifer and has the same effects as the aquifer.

A New EOR Technology: Gas Alternating Gas Injection

A new method of enhanced oil recovery has been developed and applied to a simulation using some of data from the fifth SPE paper " template from CMG ". The simulator was used in this paper is GEM in the Computer Modelling Group (CMG) advanced equation-of-state (EOS) compositional simulator. The new method is called Gas alternating gas injection(GAG). The Gas Alternating Gas process is a cyclic method of injecting alternating cycles of gas followed by gas and repeating. Sensitivity analysis showed this method can give a much better recovery factor for GAG compared with single continues gas injection. GAG benefits that will give low water cut and high oil recovery due to gas segregation between two gases and that will prevent heavier gas to go the top layers. This work indicate that the GAG injection is an economic method compared with continues injection. Especially when we use GAG (Air + CO2).&#x0D;

Fluid displacement mechanisms by foam injection within a microfluidic matrix-fracture system

In this study, the researchers visually investigated changes in the saturation of fluids and the oil recovery factor (RF) during foam injection in a two-dimensional matrix-fracture micromodel system. The effects of the 1) presence of oleic phase (comparison of the results of foam injection tests with and without oil), 2) viscous force (comparison of the results of foam and gas injection tests), and 3) gravity force (comparison of the results of gas/foam injection tests in vertical and horizontal states) were mechanistically studied. The results showed that the presence of oleic phase has the potential to cause foam to degrade at the beginning of the test. However, as the experiment advanced and oil saturation was reduced, foam injection resulted in the recovery of the fluid in the matrix. Pressure decline in the fracture due to the high viscosity of the foam acted as a driving force perpendicular to the fracture in the matrix and caused a viscous cross-flow leading to a dramatic increase in oil recovery. Although the gravity force reduced the foam stability due to the foam film drainage process and the gravity segregation of gas and surfactant solution, a comparison of the performances of gas and foam in the vertical state revealed the superiority of foam injection.

In‐situ upgrading of heavy oil using nano‐catalysts: A computational fluid dynamics study of hydrogen and vacuum residue injection

AbstractA novel nano‐catalytic in‐situ upgrading technology (ISUT) using hot fluid injection for heavy oil and bitumen production and recovery has been proposed recently (Pereira‐Almao et al., in‐situ upgrading via hot fluid injection, US Patent US20150114636A1). In this method, a vacuum distillation unit is used to separate the vacuum residue of the produced oil. The nano‐catalysts are then dispersed into the vacuum residue (VR) and are re‐injected in the reservoir, along with hydrogen. However, because of the difference in the interface forces in the residue/gas mixture, segregation of gas is possible. A practical hydrogen to VR ratio of 120 Scc/cc is employed to study the physical separation possibility within actual reservoir/well geometry. VR and hydrogen are injected at 357 and 100 °C, respectively. Computational fluid dynamics (CFD) is employed to model the VR + H2injection using the volume of fluid (VOF) method. Sensitivity analysis on reservoir pressure, mixing layout, and hydrogen solubility is also conducted.

Gas segregation during crystallization process

Analytical solution of the problem of dissolved gas segregation from melt during the crystallization process was found. The problem was solved using 3 most commonly used geometries of crystal growth: plane, cylindrical and spherical. Shrinkage of the melt during crystallization was correctly taken into account. It was shown that in the case of equilibrium crystallization the solution becomes self-similar. The criteria allowing to predict the conditions for inevitable formation of cavities in solidified material is shown.

Analytical solution of the problem of dissolved gas segregation in melt by the plain crystallization front

Analytical solution of the segregation problem is found for the arbitrary crystal growth law using the quasi-steady-state approximation. The segregation in this case is caused by the displacement of dissolved gas by moving plane crystallization front. The effect of solidification shrinkage on the crystallization process was taken into account. The comparison made between obtained solution and existing exact solutions shows good agreement. It is shown that in the case of “equilibrium crystallization” (when the growth rate is inversely proportional to time) the solution of the problem becomes self-similar. In this case gas concentration at the crystallization front instantly increases to a certain value and than stays the same during the whole process. At the same time the diffusion layer thickness increases proportionally to time. The conditions for the inevitability of gaseous release leading to the formation of pores in solidified material is formulated for the general case.

Exact solution of the problem of dissolved gas segregation by the plane crystallization front

Analytical solution of the segregation problem was found for the arbitrary crystal growth law using the quasi-steady-state approximation. The segregation is caused by the displacement of dissolved gas by moving plane crystallization front. The effect of solidification shrinkage on the crystallization process was taken into account. It is shown that in the case of “equilibrium crystallization” (when the growth rate is in inverse ratio to time) the solution of the problem becomes self-similar. In this case gas concentration at the crystallization front stays the same during the whole process while the diffusion layer thickness increases with time.